Today I received an e-mail from Cain Credicott, Co-Owner/Editor in Chief at Paleo Magazine. He contacted me because one of his editors had a question about an article on Intermittent Fasting (IF) I handed in a short while ago and that they’re now preparing to publish.
I thought the editor’s question was a great one, and one that revolves around a topic/issue that a lot of people are curious about, so I decided to put it up here on the blog.
Here’s the e-mail I got from Cain:
Hey Eirik –
Got a question from my editor on a section in this article.
(FROM YOUR ARTICLE) I would argue that we’re genetically adapted for an eating pattern that naturally incorporates periods of fasting. We should go hungry every now and then; eating all the time, and never giving our digestive machinery a rest, is unwise. This notion is supported by the evolutionary evidence, as well as a growing body of research linking IF with various health benefits, including fat loss, improved glycemic control, and reductions in blood pressure.1, 2, 5, 6
My editor is curious if you’ve examined the evidence that Stefani Ruper has brought to light re IF and women; i.e., the differential outcomes that women have on IF protocols (and the fact that most of the favorable findings involved male subjects)? Do you consider the benefits you list above to pertain to both men and women? If not, it would be great to add something about the difference between the sexes.
That’s a really interesting question. I’ve come across a couple of articles in the past that claim there’s a difference in how men and women respond to fasting, but I haven’t really dug into the literature on this issue. I took a look at the blog post you just sent over. It seems to provide a good overview of the data.
Here are my general thoughts on this issue:
Most of the scientific evidence pertaining to the health benefits of fasting is derived from studies with male participants. There’s a paucity of data on IF in relation to women’s health. Hence, it’s very difficult to draw firm conclusions regarding the health benefits of IF for women. What we can do, however, is to make educated guesses based on the evolutionary evidence, as well as the few studies on IF that have been done in women.
The author of the article at PaleoForWomen.com concludes, based on the few studies that are available, that women respond differently to fasting than men. They don’t seem to experience the same health effects, at least not to the same extent as men.
This is exactly what I would expect, based on what I know about the differences between the evolutionary path that male members of our species have traveled upon and the one that women have journeyed.
As we all know, men were historically hunters, whereas women were gatherers. When you’re out on a hunt, it may take hours or even sometimes days before you manage to chase down your prey; hence, you may go long periods of time without eating. If you get a hold of some plant foods or small game along the way, you’ll likely eat it; however, the big meal doesn’t commence until you manage to bring down your primary prey.
Some indigenous, non westernized people (e.g., the San) are known to perform persistence hunting – a type of hunting that involves tracking animals over long distances, for long periods of time, in order to completely exhaust them. It’s generally believed that this was a common hunting strategy among our Paleolithic forebears as well.
As for gathering, there isn’t one big pay-off at the end, but rather, food is gradually collected – and sometimes eaten – over time. This, in combination with the fact that pregnancies and child-rearing activities would have made our female ancestors less mobile and more dependent on a stable food supply than men, may suggest that IF agrees more with the male physiology than the female one.
Other factors may be important as well, but these are probably the major ones. Over time, these differences in the way of life of men and women would have produced physiological differences between the two sexes. For example, men developed more muscle mass in certain areas of the body than women and may have evolved an enhanced capability to sustain high levels of physical performance while in a ketogenic state. Differences in nutritional requirements (e.g., men need more protein per kilogram of body weight than women) and metabolic and hormonal responses to different meal patterns (e.g., IF) would naturally result from these physiological differences between the sexes.
Those are my general thoughts anyway. I would have to take a closer look at the literature on the topic to give you a more thorough answer.
I hope that helps!